1. Field of the Invention
This invention relates in general to gear systems and, more particularly, to a flexible pin for a helical gear system.
2. Description of the Prior Art
A special form of cantilevered support for gear elements contains a sleeve element concentric to the mounting pin that deflects in a manner that the outside of the sleeve remains parallel to the system axis. This is commonly referred to as a “flex-pin”. Such a flexpin may include an inner pin that is secured to a wall or other member, thus cantilevering the inner pin from the wall or other member, and a sleeve that is cantilevered from the opposite end of the inner pin and extends back over the inner pin, thus providing a double cantilever.
In addition to parallel deflection, these devices have an engineered spring rate to assist in equalizing load in multi-gear, split-power systems, including planetary systems. The invention disclosed in U.S. Pat. No. 3,303,713, to R. J. Hicks has significant application in heavy-duty transmissions, especially when increasing power density by using four or more planets in an epicyclical configuration. These systems normally use spur gears. With such gears, tooth contact is primarily rolling, with sliding occurring during engagement and disengagement.
In contrast helical gears are cylindrical shaped gears with helicoid teeth. Helical gears operate with less noise and vibration than spur gears. At any time, the load on helical gears is distributed over several teeth, resulting in reduced wear. Due to their angular cut, teeth meshing results in thrust loads along the gear shaft. Therefore, while helical gears have higher density and smoother operation, they generate an overturning moment in the radial plane 90° to the tangential loads that the flex-pin is designed to accommodate. With the conventional flex-pin, this moment would lead to a rotation of the gear in the radial plane that would cause tooth misalignment.
The differences in gear forces are illustrated in FIG. 1. In this Figure a planet gear is shown, which is part of an epicyclic gearing system. The ‘epicyclic’ arrangement consists of a ring of planet gears mounted on a planet carrier and meshing with a sun gear on the inside and an annulus gear on the outside. The sun and planets are external gears and the annulus is an internal gear as its teeth are on the inside. Usually either the annulus or planet carrier are held fixed, but the gear ratio is larger if the annulus is fixed.
The epicyclic arrangement allows the load to be shared out between the planets, reducing the load at any one gear interface. As can be seen in FIG. 1 there are different forces with radial (r), tangential (t) and axial (a) components acting on the planet gears in such an arrangement. For the helical gears, the axial forces result in an overturning moment.
The overturning helical gear moment can be addressed by installing reaction rings, but in practice those will encounter stress and can wear. This is particularly risky since wear particles in the area of gears and bearings are undesirable at any rate of occurrence.
Therefore, it is an object of the present invention to provide a solution to the overturning helical gear moment problem without adding components or wearing surfaces.